Inside a class body a `virtual double area() = 0;` (pure virtual), a
`virtual void draw();` and a plain prototype `int run();` parse as a
`field_declaration` whose declarator is a `function_declarator`. The field
branch recognised that shape only to skip emitting a type reference — it still
emitted a node for every declarator as a DATA MEMBER (a bare `area` label with
a `defines`/field edge).
So a pure-virtual interface class had no method nodes, only phantom fields; a
header-declared method and its out-of-line/overriding definition did not share
one node (`area` field vs `.area()` method); and a call to such a method
resolved to a field-shaped node.
Fix: in the field-declaration branch, emit a function_declarator with the same
shape a defined method uses — a `.name()` label, a `method` edge, and callable
— so the declaration and its definition collapse to one method node (parity
with the Java/TypeScript/Scala abstract-method contract). A genuine data member
still gets its `defines` field edge.
This corrects the label of every header-declared method, so a few existing
cross-file tests that asserted the old bare `bar`/`run` field label now assert
`.bar()`/`.run()`; the resolved call edges (source, target, confidence) are
unchanged, and the decl/def merge still produces exactly one node carrying the
definition site.
Added tests/test_cpp_method_declarations.py.
(cherry picked from commit 0038af9394)
